The present invention relates to a current detecting apparatus which is provided in, for example, an electric power steering apparatus of an automobile and which generates a detecting signal having electric potential proportional to magnetic flux density of a magnetic field arising from a current to be detected, and an electric motor control apparatus comprising the current detecting apparatus.
FIG. 1 is a block diagram showing one embodiment of an electric motor control apparatus comprising the conventional current detecting apparatus.
Reference numeral 10 is an electric motor control apparatus 10 which comprises an electric motor control unit 11. The electric motor control unit 11 inputs an input signal IN which is a command of a driving signal for driving an electric motor M and compares the absolute value of the electric potential of the input signal IN with the absolute value of the electric potential of a comparing signal S12. Then, it generates either a driving signal S10 for decreasing torque corresponding to the positive potential difference between the input signal IN and the comparing signal S12 or a driving signal S10 for increasing torque corresponding to the negative electric potential difference between the input signal IN and the comparing signal S12.
The electric motor M rotating by the driving signal S10 is connected to the output of the electric motor control unit 11. Further, the electric motor control apparatus 10 is provided with a current detecting apparatus (for example, a current detecting unit) 12. The current detecting unit 12 is a circuit to generate the comparing signal S12 proportional to magnetic flux density of a magnetic field B arising from the current flowing to the electric motor M driven by the driving signal S10. The current detecting unit 12 has the electric motor control unit 11 connected at the output thereof.
FIG. 2 is a circuit diagram showing one embodiment of the current detecting unit 12 of FIG. 1.
The current detecting unit 12 comprises an operational amplifier (herein under called op-amp) 12a. A noninverting input terminal of the op-amp 12a is connected to a power supply electric potential VCC through a resistor 12b and grounded through a resister 12c. An inverting input terminal of the op-amp 12a is connected to a node Ni. A positive power supply terminal of the op-amp 12a is connected to a power supply electric potential VDD and a negative power supply terminal of the op-amp 12a is grounded. A transistor 12d is connected to an output terminal of the op-amp 12a at a base thereof and connected to a node N2 at an emitter thereof. There is an input terminal of a hall sensor 12e connected between the node Ni and the node N2. The magnetic field B arising from the current which is a subject to be detected and which starts flowing to the electric motor M by the driving signal S10 is applied to the hall sensor 12e. The hall sensor 12e outputs an output signal S12e having the electric potential proportional to the magnetic flux density of the magnetic field B and a control current i supplied from the node N2. The output terminal of the hall sensor 12e is connected to an op-amp 12f for amplifying the output signal S12e by the predetermined gain and supplying the comparing signal S12. The node Ni is grounded through a resistor 12g. 
FIG. 3 is a schematic view showing one embodiment of an electric motor power steering apparatus used in an automobile utilizing the electric motor control apparatus 10 shown in FIG. 1
The electric motor power steering apparatus comprises a handle 21. The handle 21 is connected with a steering shaft 22. The steering shaft 22 is connected to a pinion 24a inside a steering gear box 24 with a coupler shaft 23 having free joints 23a, 23b at both ends. The handle 21, the steering shaft 22, the coupler shaft 23 and the steering gear box 24 constitute a hand-operated steering power generating means. The steering gear box 24 contains a rack 24b meshing into the pinion 24a. The steering power due to the handle 21 is converted into the axial direction by meshing the pinion 24a into the rack 24b to reciprocate a rack shaft 25 united with the rack 24b. The rack shaft 25 is connected to front wheels 27a, 27b at both ends thereof with tie rods 26a, 26b. 
The electric motor power steering apparatus comprises an electric motor M which is arranged in the same shaft as the rack shaft 25 and which is for applying assist torque to amplify the steering power of the hand-operated steering generation means to decrease the steering power of a driver. The electric motor M has a rotor integrated with a helical gear 28 at the driving side. The helical gear 28 meshes into a helical gear 29b integrated with one end of a screw shaft 29a of a ball screw mechanism 29. Further, The steering gear box 24 contains a steering torque detecting means 30 for detecting hand-operated steering torque of a driver acting on the pinion 24a. The electric motor control apparatus 10 of FIG. 1 is connected to the output of the steering torque detecting means 30, and the electric motor M is connected to the electric motor control apparatus 10.
In the electric power steering apparatus, the hand-operated steering torque generates as the driver operates the handle 21, and the front wheels 27a, 27b are moved to change the driving direction of the automobile. At this point, the steering torque detecting means 30 detects the hand-operated steering torque and outputs a detecting signal S30. The detecting signal S30 is applied to the electric motor control unit 11 of FIG. 1 as an input signal IN. The electric motor control unit 11 outputs the driving signal S10 corresponding to the input signal IN. The electric motor M rotates by the driving signal S10, and then the rotating torque is converted into the thrust through the helical gear 28 and the ball screw mechanism 29 to assist the thrust of the rack shaft 25. The magnetic field B arising from the current which starts flowing into the electric motor M by the driving signal S10 is applied to a hall sensor 12e of the current detecting unit 12.
In the current detecting unit 12, the electric potential of the node N2 is controlled so that the electric potential of the node Ni is equal to the reference electric potential Vr set by the resistors 12b, 12c. Further, the control current i is supplied to the node N2 from the power supply electric potential VDD. The value of the control current i is set by the resistor 12g. The control current i is applied to the hall sensor 12e, and the hall sensor 12e outputs an output signal S12e having the electric potential proportional to the control current i and the magnetic flux density of the magnetic field B. The output signal S12e is applied to the op-amp 12f and amplified, and the op-amp 12f outputs the comparing signal S12. The input signal IN is compared with the comparing signal S12 by the electric motor control unit 11. Then, if the comparing signal S12 is larger than the input signal IN, the electric motor control unit 11 outputs the driving signal S10 for decreasing torque. On the other hand, if the comparing signal S12 is smaller than the input signal IN, the electric motor control unit 11 outputs the driving signal S10 for increasing torque.
The conventional electric motor control apparatus 10 of FIG. 1 has the following problems.
FIG. 4 is a graph showing the relationship between the current IM flowing to the electric motor M and the comparing signal S12. The vertical axis indicates the electric potential of the comparing signal S12 and the horizontal axis indicates the current IM.
In FIG. 4, the assist torque is applied to the right direction with respect to the driving direction of the automobile in the positive region of the current IM and the assist torque is applied to the left direction with respect to the driving direction of the automobile in the negative region of the current IM. The characteristic line A shows the relationship between the normal current IM and the comparing signal S12. It is found that the current IM is proportional to the comparing signal S12. The characteristic line B shows the relationship between the current IM and the comparing signal S12 in a case that the control current i does not flow because of the occurrence of the damage in the current detecting unit 12. In this case, the comparing signal S12 becomes 2.5 V at all the time. However, although the current detecting unit 12 operates normally, if the current IM is zero ampere, the comparing signal S12 is 2.5V. Because of this reason, the damage of the current detecting unit 12 cannot be detected based on the value of the comparing signal S12.
To solve the problem, the damage detecting apparatus may be constituted with a computer to detect the damage of the current detecting unit 12 by analyzing the relationship between the current IM and the comparing signal S12. However, if the computer is used, the circuits are complicated and becomes large, which is unrealizable.
It is an object of the present invention to provide a current detecting apparatus having a function to determine the damage with the simple configuration and an electric motor control apparatus comprising the current detecting apparatus.
A current detecting apparatus of the present invention which comprises a hall element for outputting the change of a current to be detected as a voltage and a constant-current regulated power supply for supplying a constant current to the hall sensor comprises means for monitoring the constant current, whereby the damage of the current detecting apparatus can be detected.
The monitoring means can be an output terminal for supplying a voltage which varies according to the change of the constant current. Further, the monitoring means can be an output terminal for supplying a current from which the change of the constant current can be known. Furthermore, the current detecting apparatus may further comprises means for determining the damage of the current detecting apparatus from the change of the constant current monitored by the monitoring means.
According to the current detecting apparatus of the present invention, the damage of the constituting elements of the constant-current regulated power supply can exactly be determined with the relatively simple configuration in a short time.
An electric motor control apparatus of the present invention comprises an electric motor control unit for controlling power of a motor, and a current detecting apparatus comprising a hall element for outputting the change of a current flowing to the motor as a voltage and a constant-current regulated power supply for supplying a constant current to the hall sensor and means for monitoring the constant current, whereby the damage of the current detecting apparatus can be detected.
The monitoring means can be an output terminal for supplying a voltage which varies according to the change of the constant current. Further, the monitoring means can be an output terminal for supplying a current from which the change of the constant current can be known. Furthermore, the current detecting apparatus may further comprises means for determining the damage of the current detecting apparatus from the change of the constant current monitored by the monitoring means.
According to the electric motor control apparatus of the present invention, the damage of the constituting elements of the constant-current regulated power supply can exactly be determined with the relatively simple configuration in a short time.